Modulation system



May 31, 1927.

I L. KUHN MODULATION SYSTEM Filed Sept. 2. 1921 Ill o o u 0 w m m M 1 m mm w my 5 L w WITNESSES:

Patented May 31, 1927.

LnnwIe miner, 01* CHARLOTTENBURG, NEAR BERLIN, GERMANY, ASSIGNOR TO WEST- INGHOUSE ELECTRIC & .MANUFAQTURING COMPANY, A cORPoRATIO or rENN- SYLVANIA...

MonULATIoN sYSTEMQ Applicationfiled September 2, 1921, Serial Elm 498,185, and in Germany December 1, 1920.

by current changes in the generator and it an object of this inventionto cause the cur-- rent changes in the modulator -to produce potential changes upon. the grid of the generator in a sense that will reenforce "the current changes in the generator.

Other objects of the invention and details Of the structure will be apparent from the f ellowing description and the accompanying drawings in which the single figure is a diagrammatic view showing the connections which embody my invention. The system includes an antenna 1 having an' inductor 2, an adjustable condenser 3 and a ground connection 4. This antenna is energized by a thermionic device 5, therplate circuit of which includes a coil 6 inductively coupled to the coil 2. Anadjustable condenser 7 provides for tuning the circuit comprising the, coil 6; and thecondenser 7. The gridconnectio-n of the tube 5 inc1udes an oscillating circuit, comprising the coil 8 and the adjustable condenser 9. When the condensers 7 and 9 are properly adjusted, there is a regenerative action in thetube '5,

- due to the coupling afforded by the tube itself between the two tuned circuits.

The energy for sustaining the oscillations produced by said regenerative action 1s obtained from a battery 10. This battery is connected to theplate circuits of thegenorator tube 5 and a modulator tube 11. .The connection from the positive side of the battery'to the anodes of the tubes liand 5 includes an inductance coil ,12 having an. iron core. The purpose of this coil is to prevent any sudden change in t 1e total out put of the battery 10. The connection, common to the two late circuits of the tubes 5 and 11, inclu es a condenser 13 and goes to a point 14: in the with the resistance 15 and the. condenser 18 1n shunt with the resistance 16. the resistor 15 opposite the point 14 is connectcdtothe filament of the vacuum tube ,5 and the end of the resistor 16 opposite the point 14 is connected to the filament of the bulb 1'1. The grid of the bulb 11. is connected to the filament and this connection includes the primary 19of a transformer, the secondary of which is connected to a telephone transmitterQO. The grid connectron from the grid of the bulb 5, ends in an adjustable contact on the resistor 16, near The end of the end thereof opposite the point 14. This connection includes the os'cillatin 89'already described.

In the operation jot the'device, sounds entering the telephone transmitter 2,0, ro- -duce changes in the potential of the gri in the bulb 11 and so cause changes in the con ductivity of this bulb. Thecurrent flowing g circu t through the bulb thereupon changes and,v

since the total current is kept from changing by the inductor 12, changes of opposite sign occur in the current through the bulb 5.. These changes are; superposed upon the oscillations due to the regenerative action already described. v The energy ,deliyered to Consider the action at a time when the cnrrent in the platecircuit of the bulb 11 is increasing in response to notion of the telephone transmitter. This increase is accompanied by-an increase in the potential drop ove'r'the resistor 16. The point 14,"-sinc e it is ,connected to the ne ative end of the battery 10, may be regard d as having a constant potential. LThe filament of the tube 5, because the resistance of 15; 'is equal to the resistanceof 16, is atr -thesame potential as theright hand end of the resistor 16. The grid of the bulb 5, since it is connected to an intermediate point of the resistor 16, is. therefore,'negat1ve with respect to the filament,"-by an amount dependent upon the\ drop crease in this. drop causes the grid i'n the tube 5 to become more negative, andnegative'potential' upon the gridtends to prevent flow in theplate. circuit of the grid 5.

Increase inflow throughthe plate circuit generator and a thermionic modulator havof the bulb 11 is accompanied by diminution of the flow through the plate circuit'of the bulb 5 an'dtheaction just explained makes this diminution greater. This increase in theefi'ective resistance of the bulb 5, in its "turn, causes a further increase in the flow .When the current through in the plate circuit of the bulb 11 .It is, therefore, clear. that the changesset upby the telephone transmitter 20 give rise to a cycle of events that tends to produce further changes in the, same direction. The modulation is thus greatly increased andt'he arrangement, therefore, constitutes a very sensitive-arrangement .for sending.

the bulb 11 increases and the current through the bulb 5 decreases, the drop over the whole of'the resistor 15 is less than that over the-whole of .the'resistor 16. Ifthe connection from the grid of the bulb *5 were very close to the right hand end of the. resistor 16,'this fact would over-balance the matters just explained. If the adjustable connection of the resistor .16 were at the left hand end, no

I f 1changewhateVer in the potential of the grid ofthetube '5 would be produced by the drop in this resistor. It is, therefore, obvious fas beside the one illustrated; therefore, I dothat the extent .to which added sensitiveness is secured can be regulated by adjusting the connection along the resistor 16.

It will be evident to those skilled in the art that many variations may be made in the details of the structure and'that the invention is capable of other embodiments not intend the patent to be limited except as necessitated by the prior art andfindicated by'th claims. I f I I claim as'my invention: 11. In combination, apair of vacuum-tube devices, each having a plate circuit, a source 7 through the part'of theresistor 16 at the right of the ad ustable contact. The inof direct-current, energy connected to said plate circuits in parallel, said connection'includin a resistor, a condenser in parallel to said resistor, and a connection from the grid circuit of one of'said vacuum-tube de-- vices-to an adjustable point on said resistor. 2' In combination, a thermionic oscillation gizing said devices, a connection between the cathodes of said devices, said connection including a resistor, and means for keeping the mid-point of said resistor at the potential of the negative end of said battery.

4.; In a radio-signal-sending system, a pair of thermion c devices, a battery, a condenser, a connection between the plate circuits of saidthermionic devices, a connection hetween the cathodes of said thermionic dev1ces,sa1d last named connection includ ng a resistor, said battery and condenser each-- being connected between the mid-point of said resistor and said first named connection.

5. In combination, two thermionic devices,

each having a plate circuit, two resistors one in each of said plate circuits, two condensers, one in shunt to each of said resistors, and a connection from the grid of one of. said thermionic devices to an intermediate point in the resistor associated with the other of said thermionic devices.

' 6. In a radio system, two vacuum-tube devices, a source of direct-current potential connected to theplate circuits of said vacuum-tube' devices in parallel,- a condenser connected in parallel to said two plate circuits and connections from the grid circuit of one of said vacuum-tube devices to a point of intermediatepotential in the plate cirycuit of the other of said vacuum-tube de-' vices; 1

f In test 'ony where'oflI affix my signature. DRv Inc. LUDWIG KUHN. 

